This study will investigate the hypothesis that hyperactivity of central dopaminergic systems may be involved in the pathogenesis of stuttering and will evaluate the efficacy of dopamine blocking agents in the treatment of this disorder. Stutterers will be given injections of saline, haloperidol, promazine or apomorphine and recorded speech will be obtained 45 minutes later by a physician who is blind to the treatment. The speech will be analyzed under blind conditions to test the prediction that dopamine receptor blockade with haloperidol will be associated with clinical improvement while dopamine receptor stimulation with apomorphine will cause a transient increase in the severity of stuttering. It is not anticipated that promazine, a phenothiazine with minimal effects on dopamine recptors, wll improve speech as compared with saline placebo.